Drug delivery device

ABSTRACT

The invention refers to a drug delivery device for selecting and dispensing a number of user variable doses of a medicament. The device comprises a housing ( 10 ), a cartridge ( 170 ) containing a medicament and a last dose protection mechanism for preventing the selection of a dose, which exceeds the amount of medicament left in a cartridge ( 170 ). This last dose protection mechanism comprises a first member ( 60 ), which is rotatable in a first direction during dose selecting and in the opposite direction during dose dispensing, a second member ( 50 ) coupled to the first member ( 60 ) and to the housing ( 10 ) such that the second member is moved relative to the first member ( 60 ) and to the housing ( 10 ) upon rotation of the first member ( 60 ) and a third member ( 100 ) which is moved relative to the first and second member ( 50, 60 ) during dose dispensing. Abutment of the second and third member ( 50, 100 ) prevents increasing the selected dose.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application under 35 USC § 371of International Application No. PCT/EP2014/065338, filed on Jul. 17,2014, which claims priority to European Patent Application No.13176882.2, filed on Jul. 17, 2013, the entire contents of which areincorporated herein by reference.

The present invention is generally directed to drug delivery devices forselecting and dispensing a number of user variable doses of amedicament. In more detail, the invention refers to a drug deliverydevice having a dose limiter for preventing the setting of a dose, whichexceeds the usable amount of liquid left in a cartridge of the drugdelivery device.

Pen type drug delivery devices have application where regular injectionby persons without formal medical training occurs. This may beincreasingly common among patients having diabetes where self-treatmentenables such patients to conduct effective management of their disease.In practice, such a drug delivery device allows a user to individuallyselect and dispense a number of user variable doses of a medicament. Thepresent invention is not directed to so called fixed dose devices whichonly allow dispensing of a predefined dose without the possibility toincrease or decrease the set dose.

There are basically two types of drug delivery devices: resettabledevices (i.e., reusable) and non-resettable (i.e., disposable). Forexample, disposable pen delivery devices are supplied as self-containeddevices. Such self-contained devices do not have removable pre-filledcartridges. Rather, the pre-filled cartridges may not be removed andreplaced from these devices without destroying the device itself.Consequently, such disposable devices need not have a resettable dosesetting mechanism. The present invention is applicable for both types ofdevices, i.e. for disposable devices as well as for reusable devices.

A further differentiation of drug delivery device types refers to thedrive mechanism: There are devices which are manually driven, e.g. by auser applying a force to an injection button, devices which are drivenby a spring or the like and devices which combine these two concepts,i.e. spring assisted devices which still require a user to exert aninjection force. The spring-type devices involve springs which arepreloaded during manufacture and springs which are loaded by the userduring dose selecting. Some stored-energy devices use a combination ofspring preload and additional energy provided by the user, for exampleduring dose setting. In addition, there are further known forms ofstored energy suitable for drug delivery devices, such as compressedgas, liquid-gas phase changes, chemical reactions (pyrotechnics), motorsand solenoids with electrical power sources such as batteries. Thepresent invention is applicable for all of these types of devices, i.e.for devices with or without a drive spring or the like energy storage.

These types of pen delivery devices (so named because they oftenresemble an enlarged fountain pen) are generally comprised of threeprimary elements: a cartridge section that includes a cartridge oftencontained within a housing or holder; a needle assembly connected to oneend of the cartridge section; and a dosing section connected to theother end of the cartridge section. A cartridge (often referred to as anampoule) typically includes a reservoir that is filled with a medication(e.g., insulin), a movable rubber type bung or stopper located at oneend of the cartridge reservoir, and a top having a pierceable rubberseal located at the other, often necked-down, end. A crimped annularmetal band is typically used to hold the rubber seal in place. While thecartridge housing may be typically made of plastic, cartridge reservoirshave historically been made of glass.

The needle assembly is typically a replaceable double-ended needleassembly. Before an injection, a replaceable double-ended needleassembly is attached to one end of the cartridge assembly, a dose isset, and then the set dose is administered. Such removable needleassemblies may be threaded onto, or pushed (i.e., snapped) onto thepierceable seal end of the cartridge assembly.

The dosing section or dose setting mechanism is typically the portion ofthe pen device that is used to set (select) a dose. During an injection,a spindle or piston rod contained within the dose setting mechanismpresses against the bung or stopper of the cartridge. This force causesthe medication contained within the cartridge to be injected through anattached needle assembly. After an injection, as generally recommendedby most drug delivery device and/or needle assembly manufacturers andsuppliers, the needle assembly is removed and discarded.

Some known drug delivery devices comprise a last dose protectionmechanism for preventing the selection of a dose, which exceeds theusable amount of medicament left in a cartridge. There is a potentialhealth risk if a user may select a relatively large dose of a medicamentwhereas the amount of medicament remaining in the device—and thus theamount which is dispensed—is significantly less. Hence, such a last doseprotection mechanism is a safety feature preventing that a dose isselected which is larger than the dose which may actually be dispensedfrom the device. The usable amount of liquid may be less than the totalamount of liquid in a cartridge, for example if the amount in thenecked-down part of the cartridge cannot be fully dispensed by acartridge bung or plunger.

A disposable drug delivery device with a dose limiter is known e.g. fromWO 2004/078241 A1. The dose limiter of this device includes a last dosenut which is in threaded engagement with a drive sleeve and splined tothe housing. The drive sleeve is rotated during dose selecting andtravels only axially during dose dispensing. Rotational hard stops ofthe last dose nut and the drive sleeve interact to prevent furtherrotation of the drive sleeve relative to the housing if a user sets adose corresponding to the usable amount of liquid in the cartridge.

Further, WO 2001/019434 A1 describes an injection device with a doselimiter. The injection device is the type where a dose is set byrotating a dose setting member relative to a driver and away from afixed stop in the injection device. The dose setting member interfacesthe driver such that the dose setting member can be rotated in onedirection without rotating the driver. The dose is injected by rotatingback the dose setting member which during the backward rotation carriesthe driver with it. Rotating the driver causes the piston rod to moveforward inside the cartridge and expel some of the liquid contained inthe cartridge. The driver is provided with a track having a length whichis related to the total amount of liquid in the cartridge and whichtrack is engaged by a track follower coupled to the dose setting memberto follow rotation of this dose setting member. Each time a dose is setand injected, the track follower moves further into the track. When thetrack follower reaches the end of the track the dose setting membercannot be rotated further, and a dose larger than the remaining liquidin the cartridge cannot be set.

In some cases it might be possible for the user to over-tighten thislast dose protection mechanism resulting in device jamming.

It is an object of the present invention to provide a drug deliverydevice with an improved and reliable dose limiter, i.e. a last doseprotection mechanism.

According to a first embodiment of the present invention, this object issolved by a drug delivery device for selecting and dispensing a numberof user variable doses of a medicament comprising a housing, a cartridgecontaining a medicament and a last dose protection mechanism forpreventing the selection of a dose, which exceeds the (usable) amount ofmedicament left in a cartridge. This mechanism includes a first member,a second member and a third member. The first member is rotatable in afirst direction during dose selecting and in the opposite directionduring dose dispensing. The second member is coupled to the first memberand to the housing such that the second member is moved relative to thefirst member and to the housing upon rotation of the first member. Thethird member is moved relative to the first and second member duringdose dispensing. Abutment of the second and third member preventsincreasing the selected dose. Preferably, the movement of the first,second and third members is arranged such that the second and thirdmember abut if a pre-determined amount of medicament left in thecartridge, e.g. the usable amount which may be fully dispensed,corresponds to the actually set dose. In this embodiment the position ofthe third member within the device corresponds to the volume left in thecartridge. During dose dispensing, i.e. when the amount of medicamentdecreases in the cartridge, the third member moves into a positionreflecting the lower amount of medicament in the cartridge. As the firstmember rotates in opposite directions during dose selecting and dosedispensing, the second member shuttles back and forth depending on thedirection of rotation of the first member. Abutment of the second andthird member occurs if the third member has travelled to the vicinity ofthe second member such that the second member may interact with thethird member during dose selecting movement of the second member. Inother words, the device only detects the medicament remaining in thecartridge when the cartridge contains less than the maximum selectabledose.

The movement of the second member during dose selecting may be amovement relative to the housing in a first direction and during dosedispensing the third member may be moved relative to the housing in asecond direction which is opposite to the first direction. Preferably,during dose selecting the second member is moved axially relative to thehousing in the distal direction and during dose dispensing the thirdmember is moved axially relative to the housing in the proximaldirection. Thus, the second member approaches the third member duringdose selecting and the third member approaches the second member duringdose dispensing. However, as the second member moves in the samedirection as the third member during dose dispensing, contact betweenthe second and third member will only occur during dose selecting, wherethe third member remains stationary within the housing.

To allow the axial movements of the second and third member, the secondmember and the third member may be splined to the housing. Preferably,the second member is coupled to the first member by threads. Thisresults in an axial movement of the second member as the first memberrotates.

In an embodiment of the invention, the drug delivery device comprises alimiter mechanism defining a maximum settable dose and a minimumsettable dose. Typically, the minimum settable dose is zero (0 IU ofinsulin formulation), such that the limiter stops the device at the endof dose dispensing. The maximum settable dose, for example 60, 80 or 120IU of U300 (where U300 means 300 IU/mL) insulin formulation, may belimited to avoid overdosage. Preferably, the limits for the minimum doseand the maximum dose are provided by hard stop features.

The limiter mechanism may comprise a first member, e.g. a sleeve, whichis rotatable during dose setting and dose dispensing and which iscoupled to a dose setting member and/or to a drive member, and a secondmember, e.g. a nut, coupled to the first member and to the housing suchthat the second member is moved along a track, whose ends define themaximum dose position and the minimum dose position, with respect to thefirst member and/or the housing if the first member rotates. Thislimiter mechanism may comprise the first member and the second member ofthe last dose protection mechanism as its first and second members.Preferably, the track is a thread or a spline in the interface betweenthe sleeve and the nut.

The drug delivery device may further comprise a housing, a cartridgeholder for receiving a cartridge, a lead screw coupled to the cartridgeholder and means for driving the lead screw during dose dispensing,wherein the cartridge holder is axially displaced with respect to thehousing and the lead screw during dose dispensing. In other words, theinvention is based on the idea of retracting the cartridge with thecartridge holder instead of advancing the lead screw or piston rod.Thus, as the medication is used up the device length becomes shortermaking it more apparent to the user when a device has little medicationremaining or has been fully used. However, the bung and/or lead screw donot have to remain axially fixed relative to the housing: in someembodiments the bung and/or lead screw may move axially in addition tothe axial movement of the cartridge holder.

It is an additional benefit of retracting the cartridge, that it is moredifficult to remove the cartridge holder from the housing when thecartridge is empty. This makes tampering and counterfeiting moredifficult, and could make it impossible if the device is destroyed byremoving the cartridge holder. Further, the device length is shorter atthe end of use, so the device will take up less space in transport anddisposal at the end of its useful life. This could also reduce theperceived environmental impact of disposal.

The lead screw may be coupled to the cartridge holder by a retractionnut which is axially constrained to the cartridge holder and in threadedengagement with the lead screw. The retraction nut may have an innerthread engaging an outer thread of the lead screw. Thus, rotation of thelead screw is converted into an axial movement (retraction) of thecartridge holder. In a preferred embodiment, the retraction nut is thethird member of the last dose protection mechanism.

Independent of the above features, it is a general idea of the presentinvention to provide a drug delivery device comprising a housing, acartridge holder and a lead screw which is axially constrained withinthe housing. This allows a simplified design of the lead screw and itsattachment within the housing. As a consequence of the lead screw andthus the cartridge bung being axially fixed within the housing duringdispensing, the glass ampoule of the cartridge has to be displacedrelative to the bung and the housing.

Preferably, the cartridge holder is slidably guided in the housing androtationally constrained to the housing. For example, a bush bearing orfloating bearing may be provided for displaceably receiving thecartridge holder. In addition or as an alternative, the retraction nutmay be slidably guided in the housing and rotationally constrained tothe housing, with the cartridge holder being axially and rotationallyconstrained to the retraction nut.

To reduce the dispensing force a user has to apply, the drug deliverydevice may further comprise an elastic element such as a spring fordriving the lead screw during dose dispensing. In a disposable device,the spring may be a preloaded spring, i.e. a factory preloaded springcharged for the lifespan of the device. As an alternative, e.g. for areusable device, the spring may be loaded during dose setting andreleases the stored energy during dose dispensing. Either a disposableor a reusable device may use a combination of factory-set preload anduser-generated load of the spring. Typical spring types suitable for adrug delivery device include a torsion spring, a tension spring or thelike.

In a further embodiment, the drug delivery device comprises a displayfor indicating the selected dose. The display may have symbols, coloursor texture for indicating the selected dose and is usually visiblethrough an aperture or window of the housing.

Known devices often include a number sleeve running on a helix relativeto the housing which results in the number sleeve moving axially whichcan make the device longer. Further, the minimum axial movement islimited due requirements on the minimum text size and the maximum numberof doses which must be supported. Devices with a large number of doseswill require large axial displacements of the number sleeve, and it isdifficult to prevent numbers being shown outside the dose indicatorwindow, for example on the barrel of the number sleeve. To overcome suchdrawbacks, the display comprises at least one dose indicating elementwhich is rotatable but axially constrained in the housing. An embodimentincludes an ‘odometer’ dose indicator which only rotates, i.e. it doesnot move axially. Preferably the display comprises a first doseindicating element (first scale or single units wheel) and a second doseindicating element (second scale or tens wheel), with the first doseindicating element being coupled to the second dose indicating elementsuch that a continuous rotation of the first dose indicating element istranslated into an intermittent rotation of the second dose indicatingelement. In more detail, as the dose number is increased or reduced byrotating a dosage selector the first dose indicating element isentrained. A flexible ‘arm’ element of the first dose indicating elementmay run along a cam profile such that each time the dose selector isrotated for example 180° the flexible ‘arm’ element becomes engaged withthe second dose indicating element, i.e. the tens wheel, and indexesthis wheel by one digit.

The drug delivery device may comprise at least one clicker mechanism forgenerating a haptic and/or audible feedback. Preferably, the clickermechanism signifies the end of dose dispensing. In addition or as analternative the clicker mechanism generates a different feedback whendialling single units or given multiples of single units. In otherwords, the user hears or feels a harder ‘click’ when the set dose passesa multiple of, for example, 10 units than when it passes other units.

The drug delivery device may comprise a cartridge containing amedicament. The term “medicament”, as used herein, means apharmaceutical formulation containing at least one pharmaceuticallyactive compound,

wherein in one embodiment the pharmaceutically active compound has amolecular weight up to 1500 Da and/or is a peptide, a proteine, apolysaccharide, a vaccine, a DNA, a RNA, an enzyme, an antibody or afragment thereof, a hormone or an oligo-nucleotide, or a mixture of theabove-mentioned pharmaceutically active compound,

wherein in a further embodiment the pharmaceutically active compound isuseful for the treatment and/or prophylaxis of diabetes mellitus orcomplications associated with diabetes mellitus such as diabeticretinopathy, thromboembolism disorders such as deep vein or pulmonarythromboembolism, acute coronary syndrome (ACS), angina, myocardialinfarction, cancer, macular degeneration, inflammation, hay fever,atherosclerosis and/or rheumatoid arthritis,

wherein in a further embodiment the pharmaceutically active compoundcomprises at least one peptide for the treatment and/or prophylaxis ofdiabetes mellitus or complications associated with diabetes mellitussuch as diabetic retinopathy,

wherein in a further embodiment the pharmaceutically active compoundcomprises at least one human insulin or a human insulin analogue orderivative, glucagon-like peptide (GLP-1) or an analogue or derivativethereof, or exendin-3 or exendin-4 or an analogue or derivative ofexendin-3 or exendin-4.

Insulin analogues are for example Gly(A21), Arg(B31), Arg(B32) humaninsulin; Lys(B3), Glu(B29) human insulin; Lys(B28), Pro(B29) humaninsulin; Asp(B28) human insulin; human insulin, wherein proline inposition B28 is replaced by Asp, Lys, Leu, Val or Ala and wherein inposition B29 Lys may be replaced by Pro; Ala(B26) human insulin;Des(B28-B30) human insulin; Des(B27) human insulin and Des(B30) humaninsulin.

Insulin derivates are for example B29-N-myristoyl-des(B30) humaninsulin; B29-N-palmitoyl-des(B30) human insulin; B29-N-myristoyl humaninsulin; B29-N-palmitoyl human insulin; B28-N-myristoyl LysB28ProB29human insulin; B28-N-palmitoyl-LysB28ProB29 human insulin;B30-N-myristoyl-ThrB29LysB30 human insulin; B30-N-palmitoyl-ThrB29LysB30human insulin; B29-N-(N-palmitoyl-Y-glutamyl)-des(B30) human insulin;B29-N-(N-lithocholyl-Y-glutamyl)-des(B30) human insulin;B29-N-(ω-carboxyheptadecanoyl)-des(B30) human insulin andB29-N-(ω-carboxyhepta-decanoyl) human insulin.

Exendin-4 for example means Exendin-4(1-39), a peptide of the sequenceH-His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2.

Exendin-4 derivatives are for example selected from the following listof compounds:

H-(Lys)4-des Pro36, des Pro37 Exendin-4(1-39)-NH2,

H-(Lys)5-des Pro36, des Pro37 Exendin-4(1-39)-NH2,

des Pro36 Exendin-4(1-39),

des Pro36 [Asp28] Exendin-4(1-39),

des Pro36 [IsoAsp28] Exendin-4(1-39),

des Pro36 [Met(O)14, Asp28] Exendin-4(1-39),

des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39),

des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39),

des Pro36 [Trp(O2)25, IsoAsp28] Exendin-4(1-39),

des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39),

des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39); or

des Pro36 [Asp28] Exendin-4(1-39),

des Pro36 [IsoAsp28] Exendin-4(1-39),

des Pro36 [Met(O)14, Asp28] Exendin-4(1-39),

des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39),

des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39),

des Pro36 [Trp(O2)25, IsoAsp28] Exendin-4(1-39),

des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39),

des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39),

wherein the group -Lys6-NH2 may be bound to the C-terminus of theExendin-4 derivative;

or an Exendin-4 derivative of the sequence

des Pro36 Exendin-4(1-39)-Lys6-NH2 (AVE0010),

H-(Lys)6-des Pro36 [Asp28] Exendin-4(1-39)-Lys6-NH2,

des Asp28 Pro36, Pro37, Pro38Exendin-4(1-39)-NH2,

H-(Lys)6-des Pro36, Pro38 [Asp28] Exendin-4(1-39)-NH2,

H-Asn-(Glu)5des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-NH2,

des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2,

H-(Lys)6-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2,

H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2,

H-(Lys)6-des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2,

H-des Asp28 Pro36, Pro37, Pro38 [Trp(O2)25] Exendin-4(1-39)-NH2,

H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2,

H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28]Exendin-4(1-39)-NH2,

des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2,

H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28]Exendin-4(1-39)-(Lys)6-NH2,

H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28]Exendin-4(1-39)-(Lys)6-NH2,

H-(Lys)6-des Pro36 [Met(O)14, Asp28] Exendin-4(1-39)-Lys6-NH2,

des Met(O)14 Asp28 Pro36, Pro37, Pro38 Exendin-4(1-39)-NH2,

H-(Lys)6-desPro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2,

H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Asp28]Exendin-4(1-39)-NH2,

des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2,

H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28]Exendin-4(1-39)-(Lys)6-NH2,

H-Asn-(Glu)5 des Pro36, Pro37, Pro38 [Met(O)14, Asp28]Exendin-4(1-39)-(Lys)6-NH2,

H-Lys6-des Pro36 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2,

H-des Asp28 Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25]Exendin-4(1-39)-NH2,

H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2,

H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28]Exendin-4(1-39)-NH2,

des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28]Exendin-4(1-39)-(Lys)6-NH2,

H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28]Exendin-4(S1-39)-(Lys)6-NH2,

H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28]Exendin-4(1-39)-(Lys)6-NH2;

or a pharmaceutically acceptable salt or solvate of any one of theafore-mentioned Exendin-4 derivative.

Hormones are for example hypophysis hormones or hypothalamus hormones orregulatory active peptides and their antagonists as listed in RoteListe, ed. 2008, Chapter 50, such as Gonadotropine (Follitropin,Lutropin, Choriongonadotropin, Menotropin), Somatropine (Somatropin),Desmopressin, Terlipressin, Gonadorelin, Triptorelin, Leuprorelin,Buserelin, Nafarelin, Goserelin.

A polysaccharide is for example a glucosaminoglycane, a hyaluronic acid,a heparin, a low molecular weight heparin or an ultra low molecularweight heparin or a derivative thereof, or a sulphated, e.g. apoly-sulphated form of the above-mentioned polysaccharides, and/or apharmaceutically acceptable salt thereof. An example of apharmaceutically acceptable salt of a poly-sulphated low molecularweight heparin is enoxaparin sodium.

Antibodies are globular plasma proteins (˜150 kDa) that are also knownas immunoglobulins which share a basic structure. As they have sugarchains added to amino acid residues, they are glycoproteins. The basicfunctional unit of each antibody is an immunoglobulin (Ig) monomer(containing only one Ig unit); secreted antibodies can also be dimericwith two Ig units as with IgA, tetrameric with four Ig units liketeleost fish IgM, or pentameric with five Ig units, like mammalian IgM.

The Ig monomer is a “Y”-shaped molecule that consists of fourpolypeptide chains; two identical heavy chains and two identical lightchains connected by disulfide bonds between cysteine residues. Eachheavy chain is about 440 amino acids long; each light chain is about 220amino acids long. Heavy and light chains each contain intrachaindisulfide bonds which stabilize their folding. Each chain is composed ofstructural domains called Ig domains. These domains contain about 70-110amino acids and are classified into different categories (for example,variable or V, and constant or C) according to their size and function.They have a characteristic immunoglobulin fold in which two β sheetscreate a “sandwich” shape, held together by interactions betweenconserved cysteines and other charged amino acids.

There are five types of mammalian Ig heavy chain denoted by α, δ, ε, γ,and μ. The type of heavy chain present defines the isotype of antibody;these chains are found in IgA, IgD, IgE, IgG, and IgM antibodies,respectively.

Distinct heavy chains differ in size and composition; α and γ containapproximately 450 amino acids and δ approximately 500 amino acids, whileμ and ε have approximately 550 amino acids. Each heavy chain has tworegions, the constant region (CH) and the variable region (VH). In onespecies, the constant region is essentially identical in all antibodiesof the same isotype, but differs in antibodies of different isotypes.

Heavy chains γ, α and δ have a constant region composed of three tandemIg domains, and a hinge region for added flexibility; heavy chains μ andε have a constant region composed of four immunoglobulin domains. Thevariable region of the heavy chain differs in antibodies produced bydifferent B cells, but is the same for all antibodies produced by asingle B cell or B cell clone. The variable region of each heavy chainis approximately 110 amino acids long and is composed of a single Igdomain.

In mammals, there are two types of immunoglobulin light chain denoted byλ and κ. A light chain has two successive domains: one constant domain(CL) and one variable domain (VL). The approximate length of a lightchain is 211 to 217 amino acids. Each antibody contains two light chainsthat are always identical; only one type of light chain, κ or λ, ispresent per antibody in mammals.

Although the general structure of all antibodies is very similar, theunique property of a given antibody is determined by the variable (V)regions, as detailed above. More specifically, variable loops, threeeach the light (VL) and three on the heavy (VH) chain, are responsiblefor binding to the antigen, i.e. for its antigen specificity. Theseloops are referred to as the Complementarity Determining Regions (CDRs).Because CDRs from both VH and VL domains contribute to theantigen-binding site, it is the combination of the heavy and the lightchains, and not either alone, that determines the final antigenspecificity.

An “antibody fragment” contains at least one antigen binding fragment asdefined above, and exhibits essentially the same function andspecificity as the complete antibody of which the fragment is derivedfrom. Limited proteolytic digestion with papain cleaves the Ig prototypeinto three fragments. Two identical amino terminal fragments, eachcontaining one entire L chain and about half an H chain, are the antigenbinding fragments (Fab). The third fragment, similar in size butcontaining the carboxyl terminal half of both heavy chains with theirinterchain disulfide bond, is the crystalizable fragment (Fc). The Fccontains carbohydrates, complement-binding, and FcR-binding sites.Limited pepsin digestion yields a single F(ab′)2 fragment containingboth Fab pieces and the hinge region, including the H—H interchaindisulfide bond. F(ab′)2 is divalent for antigen binding. The disulfidebond of F(ab′)2 may be cleaved in order to obtain Fab′. Moreover, thevariable regions of the heavy and light chains can be fused together toform a single chain variable fragment (scFv).

Pharmaceutically acceptable salts are for example acid addition saltsand basic salts. Acid addition salts are e.g. HCl or HBr salts. Basicsalts are e.g. salts having a cation selected from alkali or alkaline,e.g. Na+, or K+, or Ca2+, or an ammonium ion N+(R1)(R2)(R3)(R4), whereinR1 to R4 independently of each other mean: hydrogen, an optionallysubstituted C1-C6-alkyl group, an optionally substituted C2-C6-alkenylgroup, an optionally substituted C6-C10-aryl group, or an optionallysubstituted C6-C10-heteroaryl group. Further examples ofpharmaceutically acceptable salts are described in “Remington'sPharmaceutical Sciences” 17. ed. Alfonso R. Gennaro (Ed.), MarkPublishing Company, Easton, Pa., U.S.A., 1985 and in Encyclopedia ofPharmaceutical Technology.

Pharmaceutically acceptable solvates are for example hydrates.

A non-limiting, exemplary embodiment of the invention will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 shows a sectional view of a drug delivery device in accordancewith the present invention;

FIG. 2 shows an enlarged sectional view of the drug delivery device ofFIG. 1;

FIG. 3 shows a further sectional view of the drug delivery device ofFIG. 1;

FIG. 4 shows a further enlarged sectional view of the drug deliverydevice of FIG. 1;

FIG. 5 shows cut-away views of a detail of the drug delivery device ofFIG. 1;

FIG. 6 shows a cut-away view of a further detail of the drug deliverydevice of FIG. 1;

FIG. 7 shows a cut-away view of a detail of the drug delivery device ofFIG. 1;

FIG. 8 shows a cut-away view of a detail of the drug delivery device ofFIG. 1;

FIG. 9 shows a cut-away view of a detail of the drug delivery device ofFIG. 1;

FIG. 10 shows a further enlarged sectional view of the drug deliverydevice of FIG. 1;

FIG. 11 shows a cut-away view of a detail of the drug delivery device ofFIG. 1;

FIG. 12 shows a cut-away view of a detail of the drug delivery device ofFIG. 1;

FIG. 13 shows a cut-away view of a detail of the drug delivery device ofFIG. 1;

FIG. 14 shows a sectional view of a detail of the drug delivery deviceof FIG. 1;

FIG. 15 shows a perspective view of a detail of the drug delivery deviceof FIG. 1;

FIG. 16 shows a cut-away view of a detail of the drug delivery device ofFIG. 1; and

FIG. 17 shows a perspective view of the drug delivery device of FIG. 1.

FIG. 1 shows a drug delivery device in the form of an injection pen. Thedevice has a distal end (upper end in FIG. 1) and a proximal end (lowerend in FIG. 1). The component parts of the drug delivery device areshown in FIGS. 2 to 4 in more detail. The drug delivery device comprisesa housing 10, a cartridge holder 20, a lead screw (piston rod) 30, adriver 40, a restriction nut 50, a sleeve 60, a button 70, a doseselector 80, a torsion spring 90, a retraction nut 100, a disk (antibacklash element) 110, a bezel 120, a chassis 130, a first scale 140, asecond scale 150, a return spring 160 and a cartridge 170. A needlearrangement (not shown) with a needle hub and a needle cover may beprovided as additional components, which can be exchanged as explainedabove. A last dose protection mechanism for preventing the selection ofa dose, which exceeds the (usable) amount of medicament left in thecartridge 170 includes the sleeve 60 as a first member, the restrictionnut 50 as a second member and the retraction nut 100 as a third member.

The (outer) housing 10 is a generally tubular element. In the embodimentshown in the figures, the housing 10 is a double-walled housing havingan outer housing wall 11 and an inner housing wall 12 which areconnected at the distal end of housing 10. Thus, an annular space isprovided between outer wall 11 and inner wall 12. As will be explainedbelow, torsion spring 90 is located in this annular space. The innerwall 12 is provided with an inwardly protruding flange 13 with a centralopening. Further, the inner surface of inner wall 12 is provided withribs 14 which extend in the axial (longitudinal) direction of thehousing 10. A window 15 or an aperture is located in the proximal regionof the housing 10. A transparent or translucent insert (not shown in thefigures) may be provided in the window aperture 15. As an alternative tothe embodiment depicted in the figures, outer wall 11 and inner wall 12of the housing 10 may be provided as separate components which might beuseful for manufacturing reasons. A flexible finger 16 is arrangedinside flange 13 to cooperate with a ratchet or clicker feature of leadscrew 30.

The cartridge holder 20 is located at the distal side of housing 10. Thecartridge holder may be a transparent, translucent or opaque componentwhich is tubular to receive cartridge 170. The distal end (upper end inFIG. 1) of cartridge holder 20 may be provided with means for attachinga needle arrangement. As will be explained in more detail below, thecartridge holder 20 is not rigidly fixed to housing 10, but may beretracted into housing 10. FIGS. 1 and 3 show the fully extendedposition of cartridge holder 20, whereas FIG. 17 shows the fullyretracted position of cartridge holder 20, where only the necked-downdistal end of cartridge holder 20 protrudes from housing 10. Thecartridge holder 20 is provided with snap-hooks 21 for attachingcartridge holder 20 to retraction nut 100.

The lead screw 30 is an elongate member which—in the presentembodiment—is axially fixed within the device. This is achieved by aproximal flange 31 engaging inner flange 13 of housing 10. Lead screw 30may be an injection moulded plastic component, for example made fromABS, or a metal component. An outer thread 32 is provided on lead screw30. The distal end of lead screw 30 may be provided with a bearing 33which may have the form of a disc rotatable with respect to the leadscrew 30. The proximal end of lead screw 30 is provided with a ring ofteeth 34 (face gear) located near flange 31. Lead screw 30 has a ring ofteeth 35 near its proximal end. Teeth 35 interact with finger 16 ofhousing 10 forming a clicker ratchet providing haptic and audiblefeedback during dose dispensing.

In an alternative embodiment (not shown) the bung of cartridge 170and/or lead screw 30 are allowed to move axially, in addition to theaxial movement of the cartridge 170. This axial movement may be oppositeto the movement of the cartridge 170, i.e. increasing the dispensingstroke, or in the same direction as the cartridge movement but with adifferent speed, thus reducing the dispensing stroke.

The driver 40 is a rod located in the proximal region of the device.Driver 40 has at its distal end teeth 41 (a face gear in thisembodiment, but could be internal or external teeth of a spur gear) forengaging teeth 34 of lead screw 30. Driver 40 is rotatable withinhousing 10 and may be shifted in the axial direction. FIG. 2 shows thedistal position of driver 40, where teeth 34 of the lead screw 30 engagewith teeth 41 of the driver, whereas FIG. 4 shows the proximal positionof driver 40, where teeth 34 and 41 are disengaged. An aperture 42 isprovided in the driver 40 for receiving one end of torsion spring 90. Ascan be seen in FIGS. 2 and 4, aperture 42 is provided as a slot to allowaxial movement of driver 40 without deflecting the free end of torsionspring 90. Further, three gear pinions 43, 44, 45 are located on driver40. Gear pinions 43, 44, 45 may be separate components which are rigidlyattached to the driver rod, however it is preferred to mould the rod andthe gear pinions as a unitary component. As can be seen in FIG. 15, gearpinions 43, 44, 45 may have a different diameter and a different numberof teeth. At its distal end, driver 40 carries a flange 46 which issplined to sleeve 60.

The restriction nut 50 is a sleeve-like component with an inner threadengaging sleeve 60. Further, restriction nut 50 is splined to the innersurface of inner wall 12 to prevent relative rotation betweenrestriction nut 50 and housing 10 while allowing relative axial movementof restriction nut 50 with respect to housing 10. In the embodimentshown in FIG. 6, restriction nut 50 is provided with grooves 51 engagingcorresponding ribs at the inner surface of inner wall 12. As shown inFIGS. 13 and 14, a detent 52 or protrusion is provided on the outersurface of restriction nut 50 for engaging an end of dose feature ofsleeve 60.

The sleeve 60 is a tubular dose restriction element. As can be seen inthe enlarged detail of FIG. 4, sleeve 60 has a proximal flange 61 whichis snapped into inner wall 12 of housing 10 such that sleeve 60 isaxially constrained to housing 10 but rotatable with respect to housing10. Sleeve 60 has an outer thread engaging the inner thread ofrestriction nut 50. At its inner surface, sleeve 60 is provided withribs 62 (see FIG. 14) engaging corresponding grooves in flange 46 ofdriver 40. Thus, sleeve 60 is rotationally constrained to driver 40 butallows axial displacement of driver 40 with respect to sleeve 60. Thedistal end face of sleeve 60 abuts flange 13 of housing 10 and a flangeportion at the distal end of sleeve 60 contacts flange 31 of lead screw30 to constrain lead screw 30 axially within the device. Rotational hardstops 63 are provided at either end of the outer thread of sleeve 60 torestrict movement of restriction nut 50 with respect to sleeve 60. Afinger 64 with a hook-like end is provided within flange 61. Finger 64is located such that detent 52 of restriction nut 50 contacts anddeflects finger 64 shortly before or when the proximal rotational hardstop is reached.

The button 70 forms the proximal end of the device. Button 70 has anannular skirt 71 received within dose selector 80. Further, button 70has a central stem 72 which abuts the proximal end face of driver 40.

The dose selector 80 is a sleeve-like component with a serrated outerskirt 81. A flange 82 is provided protruding inwardly at the distal endof dose selector 80 to provide a snap connection with chassis 130.Further, dose selector 80 is provided with an inner sleeve 83 having aratchet feature 84 which engages gear pinion 45 of driver 40 (see FIG.16). Ratchet feature 84 may be made as an over ratchet providing hapticand audible feedback if restriction nut 50 reached one of the rotationalheard stops of sleeve 60.

As mentioned above, the torsion spring is located between the outer wall11 and the inner wall 12 of housing 10. The distal free end of torsionspring 90 engages housing 10. The proximal free end of torsion spring 90engages aperture 42 of driver 40 as explained above. Thus, a relativerotation between driver 40 and housing 10 winds or unwinds torsionspring 90.

The retraction nut 100 is an annular element having a distal end forreceiving snap hooks 21 of the cartridge holder such that the cartridgeholder 20 is permanently attached to retraction nut 100. Alternativeembodiments may include a releasable attachment of cartridge holder 20with retraction nut 100. A central aperture of retraction nut 100 isprovided with an inner thread engaging outer thread 32 of lead screw 30.The retraction nut 100 has an outer surface which is guided within theinner wall 12 of housing 10. This outer surface includes in theembodiment shown in the figures three arms 101 which extend in theproximal direction of retraction nut 100. Further, grooves 102 areprovided in the outer surface of retraction nut 100 which engage ribs 14of the inner surface of inner wall 12. Thus, retraction nut 100 isrotationally constrained to housing 10 but is free to slide axiallywithin housing 10.

The disc 110 is provided at the distal end of lead screw 30 and servesas an anti-backlash element improving the alignment of cartridge holder20 with respect to the housing 10.

The bezel 120 is located at the distal end of housing 10. Bezel 120 issnapped onto housing 10 and comprises an opening for receiving andguiding cartridge holder 20. Thus, bezel 120 forms a bush bearing orfloating bearing for the cartridge holder 20.

The chassis 130 is rigidly attached to housing 10 and axially androtationally constrained within housing 10. Chassis 130 is provided withsnap arms 131 for attaching dose selector 80 via its flange 82. Chassis130 is provided with a central aperture receiving driver 40. Ratchetfingers 132 are provided on an inner surface of chassis 130 which engagegear pinion 44 of driver 40. Ratchet fingers 132 are designed such thata relative rotation of driver 40 with respect to chassis 130 is allowedduring dose setting and dose correction. However ratchet fingers 132couple driver 40 via gear pinion 44 to the housing 10 such that torsionspring 90 cannot overcome this ratchet. In other words, ratchet finger132 and gear pinion 44 prevent unwinding of torsion spring 90. Thisratchet may act as a clicker ratchet providing haptic and audiblefeedback during dose setting and dose correction. A distal face ofchassis 130 is provided with a cam profile 133 interacting with afeature of the first scale member 140.

The first scale member 140 is a tubular element which is rotatablyguided within housing 10. First scale 140 has an inwardly directedflange with teeth 141 which engage gear pinion 43 of driver 40. Thus,the first scale member 140 is rotationally constrained to driver 40 butallows axial displacement of the driver 40. The outer surface of thefirst scale 140 is provided with numbers or the like elements forindicating a set dose to a user. At least a portion of this outersurface is visible through window aperture 15 in housing 10. A flexiblefinger 142 is provided in the flange-like wall of the first scale 140.This finger 142 interacts with cam profile 133 of chassis 130 as thefirst scale 140 rotates with respect to chassis 130. In other words,finger 142 is deflected by cam profile 133 in the distal direction. Thecam profile 133 is designed such that finger 142 is mainly held in itssubstantially unstressed (proximal) position and is deflected only twiceper revolution in its distal position. Thus, two ramps are provided oncam profile 133 which are evenly distributed. In its deflected distalposition, finger 142 engages a corresponding feature of the second scale150 to entrain second scale 150 as the first scale 140 rotates. A detentfeature 143 may provide haptic and audible feedback during dose settingand dose correction. The first scale member 140 forms the “1 s” (Units)dose wheel of the device.

Second scale 150 is a substantially tubular element having an inwardlyprotruding flange 151 at its proximal end. Second scale 150 is rotatablyguided within housing 10 and positioned such that at least a part of theouter surface of second scale 150 is visible through window aperture 15of housing 10. Numbers or the like may be printed on this outer surfaceof second scale 150. Flange 151 is provided with recesses or a face gear152 which is positioned such that a protrusion of a flexible finger 142engages face gear 152 in the deflected distal position of finger 142.However, in the unstressed proximal position of finger 142 face gear 152is decoupled from finger 142 such that first scale 140 may rotaterelative to second scale 150. A detent feature 153 may provide hapticand audible feedback during dose setting and dose correction. The secondscale member 150 forms the “10 s” (Units) dose wheel of the device.

The return spring 160 is located between flange 31 of lead screw 30 andflange 46 of driver 40. As flange 31 rests on flange 13 of housing 10,return spring 160 biases driver 40 in the proximal direction as shown inFIG. 4. By pressing button 70, driver 40 is displaced in the distaldirection thus compressing return spring 160.

The cartridge 170 is received in cartridge holder 20. The cartridge 170may be a glass ampule having a moveable rubber bung 171 at its proximalend. The distal end of cartridge 170 is provided with a pierceablerubber seal 172 which is held in place by a crimped annular metal band.In the embodiment depicted in the figures, the cartridge 170 is astandard 1,5 ml cartridge. The device is designed to be disposable inthat the cartridge 170 cannot be replaced by the user or health careprofessional. However, a reusable variant of the device could beprovided by making the cartridge holder 120 removable and allowing theresetting of retraction nut 100.

In the following, the functioning of the disposable drug delivery deviceand its components will be explained in more detail.

When the device is at rest as shown in FIG. 3 the torsion spring 90 hasenough preload such that if the user selects the minimum dose the devicewill be able to deliver that minimum dose. At rest the dose indicator(scales 140, 150) displays 0 or the equivalent marking to show that nodose has been selected.

Priming is the act of preparing the device for first use. In existingpen injectors this means setting and delivering one or more small dosesinto air so that the ‘play’ (any clearances) and tolerances in thedevice are removed and that components are placed into suitablecompression or tension. Safety shots are where the user sets anddelivers one or more small doses into air before each injection toensure that the needle is not blocked. In the embodiment depicted in theFigures, there are no specific features that make the priming or safetyshot requirements different to those of existing pen injectors. For bothpriming the device and for safety shots, the user will set small doseand inject that dose into air and repeat until a drop of medicament isobserved at the tip of the needle.

The user sets a dose by rotating the dosage selector 80. Rotating thedosage selector rotates the driver 40 and adds preload to the torsionspring 90. The driver 40 is splined to first scale 140 and indexes whenthe user dials the dosage selector 80.

As shown in FIG. 5, the spline features (gear pinion 44) on the driver40 engage with ratchet finger 132 on the chassis 130 to prevent thedosage selector 80 rotating back to its initial position due to thetorsion spring torque. These ratchet features becomes disengaged whenthe user fully depresses the injection button 70.

Limits for setting the minimum and maximum dose (0 IU and 120 IU of U300insulin in this embodiment) are provided by hard stop features on thedose restriction nut 50 (FIGS. 9 and 12) which interfere with featureson the dose restriction sleeve 60 and therefore prevent further relativerotation. During dialling and injection the dose restriction nut 50 ismoved up and down the thread on the dose restriction sleeve 60.

A last dose protection prevents the user from setting a dose greaterthan the available volume in the cartridge 170. Many pen injectors use athreaded nut or half nut mechanism to achieve a last dose protection.Typically these mechanisms operate across the entire volume of thecartridge e.g. 3 ml for a 300 IU, U100 insulin cartridge. On somedevices it is possible for the user to over-tighten the protectionmechanism resulting in device jamming.

The embodiment of the retracting cartridge features the cartridgeretraction nut 100 which is drawn in to the device as the medication isused up. When there is less than the maximum dose remaining in thecartridge, the cartridge retraction nut 100 becomes engaged with thedose restriction nut 50 forming a rotary or an axial hard stop with thedose restriction sleeve. In other words, the device only detects themedicament remaining in the cartridge 170 when the cartridge containsless than the maximum dose (120 IU of U300 insulin formulation in thiscase).

During injection, the driver 40 is engaged with the lead screw 30. Thecartridge retraction nut 100 is threaded to the lead screw 30 andsplined to the housing 10 such that as the injection is delivered thecartridge retraction nut 100 is drawn in to the housing 10. When thecartridge volume falls below the maximum settable dose (120 IU of U300insulin formulation in this embodiment) the cartridge retraction nut 100has moved in to a position where it can interfere with the doserestriction nut 50. When the user attempts to dial a dose greater thanthat remaining, the dose restriction nut 50 interferes with the arms 101of the cartridge retraction nut 100 to form an axial hard stop as shownin FIG. 11. As an alternative, it is also possible to adapt thesefeatures to form a rotary hard stop.

Most pen injectors have a dose indicator which displays the set dose tothe user, and counts down to zero as the dose is dispensed. Most peninjectors also feature the rotation of at least one component to set thedose. The dose is normally delivered by converting the rotationalmovement of setting the dose into translation movement of the bung 171in the cartridge 170. Therefore most pen injectors feature a numbersleeve with dose indications on it which moves on a helix relative tothe housing. The problems with running the number sleeve on a helixrelative to the housing are that the number sleeve moves axially whichcan make the device longer. Further, the minimum axial movement islimited due requirements on the minimum text size and the maximum numberof doses which must be supported. Devices with a large number of doseswill require large axial displacements of the number sleeve, and it isdifficult to prevent numbers being shown outside the dose indicatorwindow, for example on the barrel of the number sleeve. The geometry ofthe text is tied to the geometry of the drive mechanism. This can limittext size or require large displacements for dose setting and injection.

To overcome such drawbacks, the embodiment of the retracting cartridgeincludes an ‘odometer’ dose indicator which only rotates, i.e. it doesnot move axially. In more detail, the dose number is increased orreduced as the dosage selector 80 is rotated. This is achieved via aspline feature (gear pinion 43 and teeth 141) between the first scalemember 140 and the driver 40. The flexible ‘arm’ element (finger 142)within the first scale member 140 runs along the cam profile 133 on thechassis 130. Each time the dose selector 80 is rotated 180° the finger142 becomes engaged with the second scale member 150, i.e. the tenswheel, and indexes this wheel by one digit. This is depicted in FIGS. 6to 8.

Most known injector pens feature a uniform level of feedback whensetting the dose, that is, the user perceives no change in sensationwhether dialling 9 units or 10 units. This results in greater dependencyon patient visual acuity and ability to process the numericalinformation shown by the dose indicator. In contrast to that with thepresent invention the patient will perceive different feedback whendialling single units or multiples of 10 units. The embodiment shownallows that the user hears or feels a harder ‘click’ when the set dosepasses a multiple of 10 units than when it passes other units. Asmentioned above, both the first and second scale members 140, 150include detent features 143, 153 which engage with correspondingelements on the inside of the housing 10. These elements are designedsuch that as each wheel 140, 150 indexes the patient will perceive adifferent level of haptic and audible feedback. For example, the firstscale member 140 (units wheel) might have a light detent whereas thesecond scale member 150 (tens wheel) may have a heavy detent.

When the injection button 70 is pressed the following actions takeplace: The driver 40 is moved forward by the injection button 70, whichcompresses the return spring 160, and engages with the lead screw 30.The driver 40 disengages from the dosage selector 80 (ratchet 84) whichmay now be rotated freely without influencing the injection or the setdose. The driver 40 moves off its ratchet (finger 132) to the chassis130 so it is free to rotate. The torsion spring 90 begins to unwindrotating the driver 40 which in turn rotates the lead screw 30. As thelead screw 30 rotates the cartridge retraction nut 100 is drawn in tothe housing 10 dispensing the medication.

If the axial force on the injection button 70 is removed, the button 70returns to its initial axial position relative to the dosage selector 80and this allows the ratchets on the driver 40 to engage with the chassis130, thus preventing further injection due to the driving torque of thetorsion spring 90. Further, this reengages the driver 40 with the dosageselector 80 thus allowing the dosage selector to set the dose again. Thedose can be changed by rotating the dosage selector 80 and pressing theinjection button 70 restarts the injection manoeuvre.

Currently most injector pens have a cartridge holder fixed rigidly tothe device body. In these devices the elastomeric bung in the cartridgeis progressed forward by a lead screw to dispense the contents. Thepresent invention features a lead screw 30 fixed axially within thedevice. When the lead screw 30 rotates during injection the cartridgeholder 20 is drawn inside the housing 10. In this case it is the bung171 which remains fixed axially and it is the cartridge 170 which moves(with the cartridge holder 20) to dispense the injection.

One of the benefits offered by retracting the cartridge 170 in to thedevice housing 10 is that the remaining dose will be more obvious to theuser. As the medication is used up the device length becomes shortermaking it more apparent to the user when a device has little medicationremaining or has been fully used. In addition, it should be moredifficult to remove the cartridge holder 20 from the housing 10. Thismakes tampering and counterfeiting more difficult, and could make itimpossible if the device is destroyed by removing the cartridge holder20. Further, the device length is shorter at the end of use, so thedevice will take up less space in transport and disposal at the end ofits useful life. This could also reduce the perceived environmentalimpact of disposal.

During injection the torsion spring 90 unwinds, rotating the driver 40.This will index the dose number mechanism such that the number countsdown towards zero. At the same time the dose restriction nut 50 movesback towards its zero position shown in FIG. 9. When the doserestriction nut 50 has reached this position the user will hear andpossibly feel a “click” to signify end of dose. This is achieved byfeatures 52 and 64 on the dose restriction nut 50 and the doserestriction sleeve 60 passing over each other with slight detentinterference (FIGS. 13 and 14).

The invention claimed is:
 1. A drug delivery device for selecting anddispensing a number of user variable doses of a medicament, the drugdelivery device comprising: a housing; a cartridge containing amedicament; and a lead screw drivable during dose dispensing to dispensethe medicament from the cartridge; a last dose protection mechanism forpreventing selection of a dose exceeding an amount of medicament left ina cartridge, wherein the last dose protection mechanism comprises: afirst member rotatable in a first direction during dose selecting and ina second direction during dose dispensing, a second member coupled tothe first member and to the housing such that the second member is movedrelative to the first member and to the housing upon rotation of thefirst member, and a third member threadedly engaged to the lead screw,the third member being movable relative to the first and second memberduring dose dispensing and configured to abut the second member toprevent increasing the selected dose.
 2. The drug delivery device ofclaim 1, wherein during dose selecting, the second member is movedrelative to the housing in a first direction and during dose dispensingthe third member is moved relative to the housing in a second directionwhich is opposite to the first direction.
 3. The drug delivery device ofclaim 2, wherein during dose selecting the second member is movedaxially relative to the housing in a distal direction and during dosedispensing the third member is moved axially relative to the housing ina proximal direction.
 4. The drug delivery device of claim 1, whereinthe second member and the third member are splined to the housing. 5.The drug delivery device of claim 1, wherein the second member iscoupled to the first member by threads.
 6. The drug delivery device ofclaim 1, comprising a limiter mechanism defining a maximum settable doseand a minimum settable dose.
 7. The drug delivery device of claim 6,wherein the limiter mechanism comprises the first member and the secondmember of the last dose protection mechanism, wherein the second memberis coupled to the first member and to the housing such that the secondmember is moved along a track, whose ends define the maximum settabledose and the minimum settable dose, with respect to at least one of thefirst member or the housing when the first member rotates.
 8. The drugdelivery device of claim 1, further comprising: a cartridge holder forreceiving the cartridge; and a driving mechanism configured to drive thelead screw during dose dispensing, wherein the lead screw is coupled tothe cartridge holder such that the cartridge holder is axially displacedwith respect to the housing and the lead screw during dose dispensing.9. The drug delivery device of claim 8, wherein the lead screw iscoupled to the cartridge holder by a retraction nut which is axiallyconstrained to the cartridge holder and in threaded engagement with thelead screw.
 10. The drug delivery device of claim 9, wherein theretraction nut is the third member of the last dose protectionmechanism.
 11. The drug delivery device of claim 1, comprising a springconfigured to drive the lead screw during dose dispensing.
 12. The drugdelivery device of claim 1, comprising a display for indicating theselected dose.
 13. The drug delivery device of claim 12, wherein thedisplay comprises at least one dose indicating element which isrotatable but axially constrained in the housing.
 14. The drug deliverydevice of claim 12, wherein the display comprises a first doseindicating element and a second dose indicating element, wherein thefirst dose indicating element is coupled to the second dose indicatingelement such that a continuous rotation of the first dose indicatingelement is translated into an intermittent rotation of the second doseindicating element.
 15. The drug delivery device of claim 1 comprisingat least one clicker mechanism for generating at least a haptic feedbackor audible feedback or the haptic feedback and the audible feedback,wherein the clicker mechanism signifies an end of dose dispensing. 16.The drug delivery device of claim 15, wherein the clicker mechanismgenerates a different feedback when dialing single units or multiples ofsingle units.
 17. The drug delivery device of claim 1, furthercomprising a cartridge holder to which the cartridge is mounted, whereinthe third member is attached to the cartridge holder.
 18. The drugdelivery device of claim 1, further comprising a drive mechanism todispense the medicament from the cartridge, wherein the first member issplined to the drive mechanism.
 19. The drug delivery device of claim 1,wherein the third member comprises a central aperture with an innerthread to engage with an outer thread of the lead screw.
 20. The drugdelivery device of claim 1, wherein an outer surface of the third membercontacts an inner wall of the housing.